Thermoplastic multi-layer golf ball

ABSTRACT

A golf ball has a relatively light core center. The golf ball may have a thermoplastic core center with diameter about 28-35 mm and flexural modulus under about 15,000 psi; a thermoplastic core layer with flexural modulus ≦about 15,000 psi and &gt;the core center&#39;s flexural modulus; and a cover ≧about 2 mm thick with specific gravity ≧about 2 g/cm 3  and flexural modulus ≧about 15,000 psi. Alternatively, the core center has diameter about 21-29 mm, flexural modulus &lt;about 15,000 psi, and specific gravity ≦about 0.95 g/cm 3 ; the core layer has specific gravity ≧about 1.1 g/cm 3  and flexural modulus ≦about 15,000 psi and &gt;the core center flexural modulus; and the cover is ≧about 1 mm thick, has specific gravity ≧about 1.1 g/cm 3 , and flexural modulus ≧about 15,000 psi.

FIELD OF THE INVENTION

The invention concerns multi-layer golf balls in which the layers havedifferent flexural moduli.

BACKGROUND

This section provides information helpful in understanding the inventionbut that is not necessarily prior art.

Golf ball core and cover layers are typically constructed with polymercompositions including, for example, polybutadiene rubber,polyurethanes, polyamides, ionomers, and blends of such polymers.Ionomers, particularly ethylene-based ionomers, are a preferred group ofpolymers for golf ball layers because of their toughness, durability,and wide range of hardness values.

Golf ball compositions comprising highly neutralized acid polymers areknown. For example, U.S. Pat. No. 7,375,151, the entire disclosure ofwhich is incorporated herein by reference, discloses a highly-resilientthermoplastic ionomer resin composition comprising (a) melt-processable,ethylene acid copolymer; (b) aliphatic, mono-functional organic acid orits salt; (c) a thermoplastic resin; (d) a cation source; and (e)optionally, a filler. The ionomer resin may be neutralized to greaterthan 90% of all the acid groups present and remain melt-processable. Thepatent discloses using the highly-resilient thermoplastic composition inone-piece, two-piece, three-piece, and multi-layered golf balls.

Differences in flexural modulus between layers in a ball with a curedrubber core have been described in Loper et al., US Patent ApplicationPublication No. 2012/0129630, for example. Weight distribution amongstthe ball layers is described, for example, in U.S. Pat. Nos. 6,193,618,5,823,889, 6,120,393, 6,142,887, and 5,984,806. Construction of athermoplastic ball, in which all layers are thermoplastic, must providegood performance characteristics to compete with rubber-containing golfballs. While various uses for highly neutralized acid polymers in golfballs have been discovered, there is a need to improve golf ballcharacteristics when using combinations of thermoplastic polymers toprovide golf ball constructions having desirable spin, feel, and CORproperties.

SUMMARY OF THE DISCLOSURE

This section provides a general summary of the disclosure and is notcomprehensive of its full scope or all of the disclosed features.

The technology now disclosed provides thermoplastic golf balls withrelatively light core centers. In a first embodiment, the golf ball hasa core center with a diameter from about 28 mm to about 35 mm includinga thermoplastic material having a flexural modulus of less than about15,000 psi; a core layer radially outward from the core center that hasa thermoplastic material with a flexural modulus of up to about 15,000psi and that is greater than the flexural modulus of the core center'sthermoplastic material; and a cover at least about 2 mm thick that has aspecific gravity of at least about 2 g/cm³ and includes a thermoplasticmaterial having a flexural modulus of at least about 15,000 psi, withthe cover forming an outermost structural layer of the ball.

In a second embodiment, a golf ball has a core center having a diameterfrom about 21 mm to about 29 mm including a thermoplastic materialhaving a flexural modulus of less than about 15,000 psi and a specificgravity of up to about 0.95 g/cm³; a core layer radially outward fromthe core center that has a specific gravity of at least about 1.1 g/cm³and including a thermoplastic material with a flexural modulus of up toabout 15,000 psi and that is greater than the flexural modulus of thecore center's thermoplastic material; and a cover that has a thicknessof at least about 1 mm, a specific gravity of at least about 1.1 g/cm³,and that includes a third thermoplastic material having a third flexuralmodulus of at least about 15,000 psi.

In these embodiments, the core center may be foamed or may include alightweight filler such as hollow glass or plastic particles or beads orfoamed particles or beads.

The ball preferably is fully thermoplastic and is free from a rubberthermoset layer.

The golf ball has a multi-layer core including a core center as aninnermost core part and one or more “core layers” outward from andenclosing the center. A “core layer” for this invention is a golf balllayer lying between the center and the cover of the golf ball. Indescribing this invention, a “cover” is the outermost structural golfball layer of the ball or, for two cover layers, each “cover layer” isone of the two outermost structural golf ball layers. Coating layers(whether paint layers or clear coating layers) are not considered to bestructural layers.

Flexural modulus is measured according to ASTM D790. Specific gravity ismeasured according to ASTM D792. “Coefficient of restitution” or COR inthe present invention is measured generally according to the followingprocedure: a golf ball is fired by an air cannon at an initial velocityof 40 msec, and a speed monitoring device is located over a distance of0.6 to 0.9 meters from the cannon. After striking a steel platepositioned about 1.2 meters away from the air cannon, the test objectrebounds through the speed-monitoring device. The return velocitydivided by the initial velocity is the COR.

“A,” “an,” “the,” “at least one,” and “one or more” are usedinterchangeably to indicate that at least one of the item is present;the indefinite articles indicate a plurality of such items may bepresent unless the context clearly indicates otherwise. All numericalvalues of parameters (e.g., of quantities or conditions) in thisspecification, including the appended claims, are to be understood asbeing modified in all instances by the term “about” whether or not“about” actually appears before the numerical value. “About” indicatesthat the stated numerical value allows some slight imprecision (withsome approach to exactness in the value; approximately or reasonablyclose to the value; nearly). If the imprecision provided by “about” isnot otherwise understood in the art with this ordinary meaning, then“about” as used herein indicates at least variations that may arise fromordinary methods of measuring and using such parameters. In addition,disclosure of ranges includes disclosure of all values and furtherdivided ranges within the entire range. Each value within a range andthe endpoints of a range are hereby all disclosed as separateembodiments. In this description of the invention, for convenience,“polymer” and “resin” are used interchangeably to encompass resins,oligomers, and polymers. The terms “comprises,” “comprising,”“including,” and “having,” are inclusive and therefore specify thepresence of stated items, but do not preclude the presence of otheritems. As used in this specification, the term “or” includes any and allcombinations of one or more of the listed items. When the terms first,second, third, etc. are used to differentiate various items from eachother, these designations are merely for convenience and do not limitthe items.

BRIEF DESCRIPTION OF THE DRAWINGS

The FIGURE is a partial cross-sectional view of an embodiment of amulti-layer golf ball that illustrates some aspects of the disclosedtechnology. The parts of the FIGURE are not necessarily to scale.

DETAILED DESCRIPTION

A detailed description of exemplary, nonlimiting embodiments follows.

As shown in the FIGURE, a multi-layer golf ball 100 has a core center110, a core layer 120 that is radially outward from the core center 110,and a cover 130 that forms the outermost layer of the golf ball 100.Each of the core center, the core layer, and the cover includes athermoplastic material.

The disclosed golf ball has a multi-layer core that includes at least acore center including a first thermoplastic material, a core layerradially outward from the core center including a second thermoplasticmaterial, and a cover including a third thermoplastic material.

Each of the first, second, and third thermoplastic materials may includeat least one thermoplastic elastomer. Each of the first, second, andthird thermoplastic materials may also include one or morenon-elastomeric polymers, plasticizers, fillers, and customaryadditives.

The first, second, and third thermoplastic materials each independentlygenerally includes at least one thermoplastic elastomer. Nonlimitingexamples of suitable thermoplastic elastomers that can be used in makingthe golf ball core and cover include metal cation ionomers of additioncopolymers (“ionomer resins”), metallocene-catalyzed block copolymers ofethylene and α-olefins having 4 to about 8 carbon atoms, thermoplasticpolyamide elastomers (e.g., polyether block polyamides), thermoplasticpolyester elastomers, thermoplastic styrene block copolymer elastomerssuch as poly(styrene-butadiene-styrene),poly(styrene-ethylene-co-butylene-styrene), andpoly(styrene-isoprene-styrene), thermoplastic polyurethane elastomers,thermoplastic polyurea elastomers, and dynamic vulcanizates of rubbersin these thermoplastic elastomers and in other thermoplastic matrixpolymers.

Ionomer resins, which are metal cation ionomers of addition copolymersof ethylenically unsaturated acids, are preferably alpha-olefin,particularly ethylene, copolymers with C₃ to C₈ α,β-ethylenicallyunsaturated carboxylic acids, particularly acrylic or methacrylic acid.The copolymers may also contain a softening monomer such as an alkylacrylate or methacrylate, for example a C₁ to C₈ alkyl acrylate ormethacrylate ester. The α,β-ethylenically unsaturated carboxylic acidmonomer may be from about 4 weight percent or about 6 weight percent orabout 8 weight percent up to about 20 weight percent or up to about 35weight percent of the copolymer, and the softening monomer, whenpresent, is preferably present in a finite amount, preferably at leastabout 5 weight percent or at least about 11 weight percent, up to about23 weight percent or up to about 25 weight percent or up to about 50weight percent of the copolymer.

Nonlimiting specific examples of acid-containing ethylene copolymersinclude copolymers of ethylene/acrylic acid/n-butyl acrylate,ethylene/methacrylic acid/n-butyl acrylate, ethylene/methacrylicacid/isobutyl acrylate, ethylene/acrylic acid/isobutyl acrylate,ethylene/methacrylic acid/n-butyl methacrylate, ethylene/acrylicacid/methyl methacrylate, ethylene/acrylic acid/methyl acrylate,ethylene/methacrylic acid/methyl acrylate, ethylene/methacrylicacid/methyl methacrylate, and ethylene/acrylic acid/n-butylmethacrylate. Preferred acid-containing ethylene copolymers includecopolymers of ethylene/methacrylic acid/n-butyl acrylate,ethylene/acrylic acid/n-butyl acrylate, ethylene/methacrylic acid/methylacrylate, ethylene/acrylic acid/ethyl acrylate, ethylene/methacrylicacid/ethyl acrylate, and ethylene/acrylic acid/methyl acrylate. Invarious embodiments the most preferred acid-containing ethylenecopolymers include ethylene/(meth)acrylic acid/n-butyl acrylate,ethylene/(meth)acrylic acid/ethyl acrylate, and ethylene/(meth)acrylicacid/methyl acrylate copolymers.

The ionomer resin may be a high acid ionomer resin. In general, ionomersprepared by neutralizing acid copolymers including at least about 16weight % of copolymerized acid residues based on the total weight of theunneutralized ethylene acid copolymer are considered “high acid”ionomers. In these high modulus ionomers, the acid monomer, particularlyacrylic or methacrylic acid, is present in about 16 to about 35 weight%. In various embodiments, the copolymerized carboxylic acid may be fromabout 16 weight %, or about 17 weight % or about 18.5 weight % or about20 weight % up to about 21.5 weight % or up to about 25 weight % or upto about 30 weight % or up to about 35 weight % of the unneutralizedcopolymer. A high acid ionomer may be combined with a “low acid” ionomerin which the copolymerized carboxylic acid is less than 16 weight % ofthe unneutralized copolymer. Such a mixture of a high acid ionomer and alow acid ionomer is particularly suitable for the third thermoplasticmaterial of the inner cover layer or the fourth thermoplastic materialor the outer cover layer, and especially for the third thermoplasticmaterial of the inner cover layer.

The acid moiety in the ethylene-acid copolymer is neutralized by anymetal cation. Suitable preferred cations include lithium, sodium,potassium, magnesium, calcium, barium, lead, tin, zinc, aluminum, or acombination of these cations; in various embodiments alkali metal,alkaline earth metal, or zinc cations are particularly preferred. Invarious embodiments, the acid groups of the ionomer may be neutralizedfrom about 10% or from about 20% or from about 30% or from about 40% toabout 60% or to about 70% or to about 75% or to about 80% or to about90%.

A sufficiently high molecular weight, monomeric organic acid or salt ofsuch an organic acid may be added to the acid copolymer or ionomer sothat the acid copolymer or ionomer can be neutralized, without losingprocessability, to a level above the level that would cause the ionomeralone to become non-melt-processable. The high-molecular weight,monomeric organic acid its salt may be added to the ethylene-unsaturatedacid copolymers before they are neutralized or after they are optionallypartially neutralized to a level between about 1 and about 100%,provided that the level of neutralization is such that the resultingionomer remains melt-processable. In generally, when the high-molecularweight, monomeric organic acid is included the acid groups of thecopolymer may be neutralized from at least about 40 to about 100%,preferably from at least about 90% to about 100%, and most preferably100% without losing processability. Such high neutralization,particularly to levels greater than 80%, greater than 90% or greaterthan 95% or most preferably 100%, without loss of processability can bedone by (a) melt-blending the ethylene α,β-ethylenically unsaturatedcarboxylic acid copolymer or a melt-processable salt of the copolymerwith an organic acid or a salt of organic acid, and (b) adding asufficient amount of a cation source up to 110% of the amount needed toneutralize the total acid in the copolymer or ionomer and organic acidor salt to the desired level to increase the level of neutralization ofall the acid moieties in the mixture preferably to greater than 90%,preferably greater than 95%, or preferably to 100%. To obtain 100%neutralization, it is preferred to add a slight excess of up to 110% ofcation source over the amount stoichiometrically required to obtain the100% neutralization.

The high molecular weight, monomeric saturated or unsaturated acid mayhave from 8 or 12 or 18 carbon atoms to 36 carbon atoms or to less than36 carbon atoms. Nonlimiting suitable examples of the high-molecularweight, monomeric saturated or unsaturated organic acids includestearic, behenic, erucic, oleic, and linoleic acids and their salts,particularly the barium, lithium, sodium, zinc, bismuth, chromium,cobalt, copper, potassium, strontium, titanium, tungsten, magnesium, orcalcium salts of these fatty acids. These may be used in combinations.

Thermoplastic polyolefin elastomers may also be used in thethermoplastic materials of the golf ball. These aremetallocene-catalyzed block copolymers of ethylene and α-olefins having4 to about 8 carbon atoms that are prepared by single-site metallocenecatalysis, for example in a high pressure process in the presence of acatalyst system comprising a cyclopentadienyl-transition metal compoundand an alumoxane. Nonlimiting examples of the α-olefin softeningcomonomer include hexane-1 or octene-1; octene-1 is a preferredcomonomer to use. These materials are commercially available, forexample, from ExxonMobil under the tradename Exact™ and from the DowChemical Company under the tradename Engage™.

Suitable thermoplastic styrene block copolymer elastomers that may beused in the thermoplastic materials of the golf ball includepoly(styrene-butadiene-styrene),poly(styrene-ethylene-co-butylene-styrene),poly(styrene-isoprene-styrene), and poly(styrene-ethylene-co-propylene)copolymers. These styrenic block copolymers may be prepared by livinganionic polymerization with sequential addition of styrene and the dieneforming the soft block, for example using butyl lithium as initiator.Thermoplastic styrene block copolymer elastomers are commerciallyavailable, for example, under the trademark Kraton™ sold by KratonPolymers U.S. LLC, Houston, Tex. Other such elastomers may be made asblock copolymers by using other polymerizable, hard, non-rubber monomersin place of the styrene, including meth(acrylate) esters such as methylmethacrylate and cyclohexyl methacrylate, and other vinyl arylenes, suchas alkyl styrenes.

Thermoplastic polyurethane elastomers such as thermoplasticpolyester-polyurethanes, polyether-polyurethanes, andpolycarbonate-polyurethanes may be used in the thermoplastic materials,particularly in the third thermoplastic material for the cover. Thethermoplastic polyurethane elastomers include polyurethanes polymerizedusing as polymeric diol reactants polyethers and polyesters includingpolycaprolactone polyesters. These polymeric diol-based polyurethanesare prepared by reaction of the polymeric diol (polyester diol,polyether diol, polycaprolactone diol, polytetrahydrofuran diol, orpolycarbonate diol), one or more polyisocyanates, and, optionally, oneor more chain extension compounds. Chain extension compounds, as theterm is being used, are compounds having two or more functional groupsreactive with isocyanate groups, such as the diols, amino alcohols, anddiamines. Preferably the polymeric diol-based polyurethane issubstantially linear (i.e., substantially all of the reactants aredifunctional).

Diisocyanates used in making the polyurethane elastomers may be aromaticor aliphatic. Useful diisocyanate compounds used to preparethermoplastic polyurethanes include, without limitation, isophoronediisocyanate (IPDI), methylene bis-4-cyclohexyl isocyanate (H₁₂MDI),cyclohexyl diisocyanate (CHDI), m-tetramethyl xylene diisocyanate(m-TMXDI), p-tetramethyl xylene diisocyanate (p-TMXDI), 4,4′-methylenediphenyl diisocyanate (MDI, also known as 4,4′-diphenylmethanediisocyanate), 2,4- or 2,6-toluene diisocyanate (TDI), ethylenediisocyanate, 1,2-diisocyanatopropane, 1,3-diisocyanatopropane,1,6-diisocyanatohexane (hexamethylene diisocyanate or HDI), 1,4-butylenediisocyanate, lysine diisocyanate, meta-xylylenediioscyanate andpara-xylylenediisocyanate (XDI), 4-chloro-1,3-phenylene diisocyanate,1,5-tetrahydro-naphthalene diisocyanate, 4,4′-dibenzyl diisocyanate, andcombinations of these. Nonlimiting examples of higher-functionalitypolyisocyanates that may be used in limited amounts to produce branchedthermoplastic polyurethanes (optionally along with monofunctionalalcohols or monofunctional isocyanates) include 1,2,4-benzenetriisocyanate, 1,3,6-hexamethylene triisocyanate, 1,6,11-undecanetriisocyanate, bicycloheptane triisocyanate,triphenylmethane-4,4′,4″-triisocyanate, isocyanurates of diisocyanates,biurets of diisocyanates, allophanates of diisocyanates, and the like.

Nonlimiting examples of suitable diols that may be used as extendersinclude ethylene glycol and lower oligomers of ethylene glycol includingdiethylene glycol, triethylene glycol, and tetraethylene glycol;propylene glycol and lower oligomers of propylene glycol includingdipropylene glycol, tripropylene glycol, and tetrapropylene glycol;cyclohexanedimethanol, 1,6-hexanediol, 2-ethyl-1,6-hexanediol,1,4-butanediol, 2,3-butanediol, 1,5-pentanediol, 1,3-propanediol,butylene glycol, neopentyl glycol, dihydroxyalkylated aromatic compoundssuch as the bis(2-hydroxyethyl) ethers of hydroquinone and resorcinol;p-xylene-α,α′-diol; the bis(2-hydroxyethyl) ether of p-xylene-α,α′-diol;m-xylene-α,α′-diol, and combinations of these. Other activehydrogen-containing chain extenders that contain at least two activehydrogen groups may be used, for example, dithiols, diamines, orcompounds having a mixture of hydroxyl, thiol, and amine groups, such asalkanolamines, aminoalkyl mercaptans, and hydroxyalkyl mercaptans, amongothers. Suitable diamine extenders include, without limitation, ethylenediamine, diethylene triamine, triethylene tetraamine, and combinationsof these. Other typical chain extenders are amino alcohols such asethanolamine, propanolamine, butanolamine, and combinations of these.The molecular weights of the chain extenders preferably range from about60 to about 400. Alcohols and amines are preferred.

In addition to difunctional extenders, a small amount of a trifunctionalextender such as trimethylolpropane, 1,2,6-hexanetriol and glycerol, ormonofunctional active hydrogen compounds such as butanol ordimethylamine, may also be included. The amount of trifunctionalextender or monofunctional compound employed may be, for example, 5.0equivalent percent or less based on the total weight of the reactionproduct and active hydrogen containing groups used.

The polyester diols used in forming a thermoplastic polyurethaneelastomer are in general prepared by the condensation polymerization ofone or more polyacid compounds and one or more polyol compounds.Preferably, the polyacid compounds and polyol compounds aredi-functional, i.e., diacid compounds and diols are used to preparesubstantially linear polyester diols, although minor amounts ofmono-functional, tri-functional, and higher functionality materials canbe included to provide a slightly branched, but uncrosslinked polyesterpolyol component. Suitable dicarboxylic acids include, withoutlimitation, glutaric acid, succinic acid, malonic acid, oxalic acid,phthalic acid, isophthalic acid, hexahydrophthalic acid, adipic acid,maleic acid, suberic acid, azelaic acid, dodecanedioic acid, theiranhydrides and polymerizable esters (e.g., methyl esters) and acidhalides (e.g., acid chlorides), and mixtures of these. Suitable polyolsinclude those already mentioned, especially the diols. Typical catalystsfor the esterification polymerization are protonic acids, Lewis acids,titanium alkoxides, and dialkyltin oxides.

A polymeric polyether or polycaprolactone diol reactant for preparingthermoplastic polyurethane elastomers may be obtained by reacting a diolinitiator, e.g., 1,3-propanediol or ethylene or propylene glycol, with alactone or alkylene oxide chain-extension reagent. Lactones that can bering opened by an active hydrogen are well-known in the art. Examples ofsuitable lactones include, without limitation, ε-caprolactone,γ-caprolactone, β-butyrolactone, β-propriolactone, γ-butyrolactone,α-methyl-γ-butyrolactone, β-methyl-γ-butyrolactone, γ-valerolactone,δ-valerolactone, γ-decanolactone, δ-decanolactone, γ-nonanoic lactone,γ-octanoic lactone, and combinations of these. In one preferredembodiment, the lactone is ε-caprolactone. Useful catalysts includethose mentioned above for polyester synthesis. Alternatively, thereaction can be initiated by forming a sodium salt of the hydroxyl groupon the molecules that will react with the lactone ring. In otherembodiments, a diol initiator may be reacted with an oxirane-containingcompound or cyclic ether to produce a polyether diol to be used in thepolyurethane elastomer polymerization. Alkylene oxide polymer segmentsinclude, without limitation, the polymerization products of ethyleneoxide, propylene oxide, 1,2-cyclohexene oxide, 1-butene oxide, 2-buteneoxide, 1-hexene oxide, tert-butylethylene oxide, phenyl glycidyl ether,1-decene oxide, isobutylene oxide, cyclopentene oxide, 1-pentene oxide,and combinations of these. The oxirane- or cyclic ether-containingcompound is preferably selected from ethylene oxide, propylene oxide,butylene oxide, tetrahydrofuran, and combinations of these. The alkyleneoxide polymerization is typically base-catalyzed. The polymerization maybe carried out, for example, by charging the hydroxyl-functionalinitiator compound and a catalytic amount of caustic, such as potassiumhydroxide, sodium methoxide, or potassium tert-butoxide, and adding thealkylene oxide at a sufficient rate to keep the monomer available forreaction. Two or more different alkylene oxide monomers may be randomlycopolymerized by coincidental addition or polymerized in blocks bysequential addition. Homopolymers or copolymers of ethylene oxide orpropylene oxide are preferred. Tetrahydrofuran may be polymerized by acationic ring-opening reaction using such counterions as SbF₆ ⁻, AsF₆ ⁻,PF₆ ⁻, SbCl₆ ⁻, BF₄ ⁻, CF₃SO₃ ⁻, FSO₃ ⁻, and ClO₄ ⁻. Initiation is byformation of a tertiary oxonium ion. The polytetrahydrofuran segment canbe prepared as a “living polymer” and terminated by reaction with thehydroxyl group of a diol such as any of those mentioned above.Polytetrahydrofuran is also known as polytetramethylene ether glycol(PTMEG).

Aliphatic polycarbonate diols that may be used in making a thermoplasticpolyurethane elastomer may be prepared by the reaction of diols withdialkyl carbonates (such as diethyl carbonate), diphenyl carbonate, ordioxolanones (such as cyclic carbonates having five- and six-memberrings) in the presence of catalysts like alkali metal, tin catalysts, ortitanium compounds. Useful diols include, without limitation, any ofthose already mentioned. Aromatic polycarbonates are usually preparedfrom reaction of bisphenols, e.g., bisphenol A, with phosgene ordiphenyl carbonate.

In various embodiments, the polymeric diol preferably has a weightaverage molecular weight of at least about 500, more preferably at leastabout 1000, and even more preferably at least about 1800 and a weightaverage molecular weight of up to about 10,000, but polymeric diolshaving weight average molecular weights of up to about 5000, especiallyup to about 4000, may also be preferred. The polymeric dioladvantageously has a weight average molecular weight in the range fromabout 500 to about 10,000, preferably from about 1000 to about 5000, andmore preferably from about 1500 to about 4000. The weight averagemolecular weights may be determined by ASTM D4274.

The reaction of the polyisocyanate, polymeric diol, and diol or otherchain extension agent is typically carried out at an elevatedtemperature in the presence of a catalyst. Typical catalysts for thisreaction include organotin catalysts such as stannous octoate, dibutyltin dilaurate, dibutyl tin diacetate, dibutyl tin oxide, tertiaryamines, zinc salts, and manganese salts. Generally, for elastomericpolyurethanes, the ratio of polymeric diol, such as polyester diol, toextender can be varied within a relatively wide range depending largelyon the desired flexural modulus of the final polyurethane elastomer. Forexample, the equivalent proportion of polyester diol to extender may bewithin the range of 1:0 to 1:12 and, more preferably, from 1:1 to 1:8.Preferably, the diisocyanate(s) employed are proportioned such that theoverall ratio of equivalents of isocyanate to equivalents of activehydrogen containing materials is within the range of 1:1 to 1:1.05, andmore preferably, 1:1 to 1:1.02. The polymeric diol segments typicallyare from about 35% to about 65% by weight of the polyurethane polymer,and preferably from about 35% to about 50% by weight of the polyurethanepolymer.

Suitable thermoplastic polyurea elastomers may be prepared by reactionof one or more polymeric diamines or polyols with one or more of thepolyisocyanates already mentioned and one or more diamine extenders.Nonlimiting examples of suitable diamine extenders include ethylenediamine, 1,3-propylene diamine, 2-methyl-pentamethylene diamine,hexamethylene diamine, 2,2,4- and 2,4,4-trimethyl-1,6-hexane diamine,imino-bis(propylamine), imido-bis(propylamine),N-(3-aminopropyl)-N-methyl-1,3-propanediamine),1,4-bis(3-aminopropoxy)butane, diethyleneglycol-di(aminopropyl)ether),1-methyl-2,6-diamino-cyclohexane, 1,4-diamino-cyclohexane, 1,3- or1,4-bis(methylamino)-cyclohexane, isophorone diamine, 1,2- or1,4-bis(sec-butylamino)-cyclohexane, N,N′-diisopropyl-isophoronediamine, 4,4′-diamino-dicyclohexylmethane,3,3′-dimethyl-4,4′-diamino-dicyclohexylmethane,N,N′-dialkylamino-dicyclohexylmethane, and3,3′-diethyl-5,5′-dimethyl-4,4′-diamino-dicyclohexylmethane. Polymericdiamines include polyoxyethylene diamines, polyoxypropylene diamines,poly(oxyethylene-oxypropylene) diamines, and poly(tetramethylene ether)diamines. The amine- and hydroxyl-functional extenders already mentionedmay be used as well. Generally, as before, trifunctional reactants arelimited and may be used in conjunction with monofunctional reactants toprevent crosslinking.

Suitable thermoplastic polyamide elastomers may be obtained by: (1)polycondensation of (a) a dicarboxylic acid, such as oxalic acid, adipicacid, sebacic acid, terephthalic acid, isophthalic acid,1,4-cyclohexanedicarboxylic acid, or any of the other dicarboxylic acidsalready mentioned with (b) a diamine, such as ethylenediamine,tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, ordecamethylenediamine, 1,4-cyclohexanediamine, m-xylylenediamine, or anyof the other diamines already mentioned; (2) a ring-openingpolymerization of a cyclic lactam, such as ε-caprolactam orω-laurolactam; (3) polycondensation of an aminocarboxylic acid, such as6-aminocaproic acid, 9-aminononanoic acid, 11-aminoundecanoic acid, or12-aminododecanoic acid; or (4) copolymerization of a cyclic lactam witha dicarboxylic acid and a diamine to prepare a carboxylicacid-functional polyamide block, followed by reaction with a polymericether diol (polyoxyalkylene glycol) such as any of those alreadymentioned. Polymerization may be carried out, for example, attemperatures of from about 180° C. to about 300° C. Specific examples ofsuitable polyamide block copolymers include NYLON 6, NYLON 66, NYLON610, NYLON 11, NYLON 12, copolymerized NYLON MXD6, and NYLON 46 basedelastomers. Thermoplastic poly(ether amide) block copolymer elastomers(PEBA) are commercially available under the trademark Pebax® fromArkema.

Thermoplastic polyester elastomers have blocks of monomer units with lowchain length that form the crystalline regions and blocks of softeningsegments with monomer units having relatively higher chain lengths.Thermoplastic polyester elastomers are commercially available under thetrademark Hytrel® from DuPont.

The thermoplastic materials of the golf ball may include combinations ofthermoplastic elastomers. In one embodiment, a thermoplastic materialincludes a combination of a metal ionomer of a copolymer of ethylene andat least one of acrylic acid and methacrylic acid, ametallocene-catalyzed copolymer of ethylene and an α-olefin having 4 toabout 8 carbon atoms, and a metal salt of an unsaturated fatty acid.This material may be prepared as described in Statz et al., U.S. Pat.No. 7,375,151 or as described in Kennedy, “Process for MakingThermoplastic Golf Ball Material and Golf Ball with ThermoplasticMaterial, U.S. patent application Ser. No. 13/825,112, filed 15 Mar.2013, the entire contents of both being incorporated herein byreference.

In various embodiments, the first thermoplastic material includes anionomer resin and a polyolefin elastomer. In various embodiments, atleast one of the first thermoplastic material, the second thermoplasticmaterial, and the third thermoplastic material includes a polymerselected from ionomer resins, polyamide elastomers, polyurethaneelastomers, thermoplastic polyester elastomers, and combinations ofthese.

The thermoplastic materials may include other polymers. In one example,the first or second thermoplastic material may include dispersed domainsof cured rubbers, which may be incorporated in a thermoplastic elastomermatrix via dynamic vulcanization of rubbers in any of thesethermoplastic elastomers or in other thermoplastic polymers. One suchcomposition is described in Voorheis et al, U.S. Pat. No. 7,148,279,which is incorporated herein by reference. In various embodiments, thefirst thermoplastic material may include a thermoplastic dynamicvulcanizate of a rubber in a non-elastomeric matrix resin such aspolypropylene. Thermoplastic vulcanizates commercially available fromExxonMobil under the tradename Santoprene™ are believed to be vulcanizeddomains of EPDM in polypropylene.

Depending on the elastomer selected for each thermoplastic material, oneor more plasticizers may be incorporated. One example of such aplasticizer is the high molecular weight, monomeric organic acid or itssalt that may be incorporated, for example, with an ionomer polymer asalready described, including metal stearates such as zinc stearate,calcium stearate, barium stearate, lithium stearate and magnesiumstearate. For most thermoplastic elastomers, the percentage ofhard-to-soft segments is adjusted if lower hardness is desired ratherthan by adding a plasticizer.

The second thermoplastic material's flexural modulus is greater than thefirst thermoplastic material's flexural modulus. The secondthermoplastic material's flexural modulus is up to about 15,000 psi andthe first thermoplastic material's flexural modulus is less than about15,000 psi, preferably up to about 10,000 psi, and less than the secondthermoplastic material's flexural modulus. In certain preferredembodiments, the first flexural modulus is from about 1,000 psi to lessthan about 15,000 psi, more preferably from about 3000 psi to about 6000psi and the second flexural modulus is from about 1,000 psi to about15,000 psi, more preferably from about 6000 psi to about 12,000 psi.

Nonlimiting examples of thermoplastic polymers that may be used thathave a flexural modulus up to about 15,000 are the grades of ionomerresins sold by DuPont Company, Wilmington Del. under the name Surlyn®6320, 8020, 8120, 8320, 9020, 9320, and 9320W, and DuPont's HPF2000 andHPF AD1035 ionomer resins; polyolefin elastomers such as Engage™ 8180;thermoplastic polyester polyurethanes and thermoplastic polyetherpolyurethanes, including G35D50N and G38D50N, sold by Hwa Pao ResinsChemical Co. Ltd. The thermoplastic polymers may be mixed with an amountof filler or other polymers that results in the flexural modulus of thethermoplastic material having the desired value for flexural modulus.

The polymers and the type and amount of any filler of each of the first,second, and third thermoplastic materials are selected and apportionedso that the flexural moduli and specific gravities have a desiredrelationship.

The third thermoplastic material has a third flexural modulus of atleast about 15,000 psi. In other embodiments, the third flexural modulusmay be at least about 35,000 psi. In various embodiments, the cover hasa specific gravity of from about 2.0 g/cm³ to about 3.0 g/cm³,preferably from about 2.0 g/cm³ to about 2.5 g/cm³.

The third thermoplastic material may include a filler to increase thethird flexural modulus. Preferably, the third thermoplastic materialincludes a metal or metal compound such as a metal oxide. Nonlimitingexamples of heavy-weight fillers that may be used to increase specificgravity include titanium, tungsten, aluminum, bismuth, nickel,molybdenum, iron, steel, lead, copper, brass, boron, boron carbidewhiskers, bronze, cobalt, beryllium, zinc, tin, and metal oxides (suchas zinc oxide, iron oxide, aluminum oxide, titanium oxide, magnesiumoxide, zirconium oxide).

Various fillers may be included in the first and second thermoplasticmaterials, and the filler may also be selected to modify the specificgravity, hardness, or other properties of the thermoplastic material.Nonlimiting examples of suitable fillers include clay, talc, asbestos,graphite, glass, mica, calcium metasilicate, barium sulfate, zincsulfide, aluminum hydroxide, silicates, diatomaceous earth, carbonates(such as calcium carbonate, magnesium carbonate and the like), metals(such as titanium, tungsten, aluminum, bismuth, nickel, molybdenum,iron, copper, brass, boron, bronze, cobalt, beryllium and alloys ofthese), metal oxides (such as zinc oxide, iron oxide, aluminum oxide,titanium oxide, magnesium oxide, zirconium oxide and the like),particulate synthetic plastics (such as high molecular weightpolyethylene, polystyrene, polyethylene ionomeric resins and the like),particulate carbonaceous materials (such as carbon black, naturalbitumen and the like), as well as cotton flock, cellulose flock and/orleather fiber. In particular, the first thermoplastic material mayinclude a light-weight filler. Nonlimiting examples of light-weightfillers that may be used to decrease specific gravity includeparticulate plastics, glass, ceramics, and hollow spheres, regrinds, orfoams of these. Fillers that may be used in the core center and corelayers of a golf ball are typically in a finely divided form.

The cover may be formulated with a pigment, such as a yellow or whitepigment, and in particular a white pigment such as titanium dioxide orzinc oxide. Generally titanium dioxide is used as a white pigment, forexample in amounts of from about 0.5 parts by weight or 1 part by weightto about 8 parts by weight or 10 parts by weight based on 100 parts byweight of polymer. In various embodiments, a white-colored cover may betinted with a small amount of blue pigment or brightener.

In other embodiments, each of the core layer and the cover independentlyhas a specific gravity of at least about 1.1 g/cm³, preferably fromabout 1.1 g/cm³ to about 1.8 g/cm³. These specific gravities may beobtained by incorporating one or more fillers, preferably one or moreheavy-weight fillers such as those already mentioned. When each of thecore layer and the cover independently has a specific gravity of atleast about 1.1 g/cm³, the core center has a specific gravity of up toabout 0.95 g/cm³. The first thermoplastic material making up the corecenter may be foamed or include lightweight fillers. Nonlimitingexamples of light-weight fillers that may be used to decrease specificgravity include particulate plastics, glass, ceramics, and hollowspheres, regrinds, or foams. The first thermoplastic material can befoamed using techniques well-known in the art. In one method, a chemicalor mechanical blowing agent is incorporated into the first thermoplasticmaterial, causing the first thermoplastic material to foam when it ismolded into the core center. Suitable examples of blowing agents thatmay be used include 2,2′-azo-bis(isobutyronitrile), azodicarbonamide,4,4′-oxy-bis(benzenesulfonyl hydrazide) anddinitrosopentamethylenetetramine. In another method, the firstthermoplastic material is infused with a supercritical fluid in apressurized container, then rapidly depressurized and heated either byimmersion in a heated fluid that can rapidly heat the article or withinfrared or microwave radiation to heat and foam the first thermoplasticmaterial. Nonlimiting examples of suitable compounds that can be used asthe supercritical fluid include carbon dioxide (critical temperature31.1° C., critical pressure 7.38 MPa), nitrous oxide (criticaltemperature 36.5° C., critical pressure 7.24 MPa), ethane (criticaltemperature 32.3° C., critical pressure 4.88 MPa), ethylene (criticaltemperature 9.3° C., critical pressure 5.12 MPa), nitrogen (criticaltemperature −147° C., critical pressure 3.39 MPa), oxygen (criticaltemperature −118.6° C., critical pressure 5.08 MPa), ammonia (criticaltemperature 132.5° C., critical pressure 11.28 MPa), and water (criticaltemperature 374.2° C., critical pressure 22.12 psi). Supercriticalcarbon dioxide is one particularly preferred supercritical fluid. Thearticle of first thermoplastic material that is foamed may be anelastomeric material in the general shape of the core center when it isinfused with the supercritical fluid so that foaming results in theformed foam core center. The core center may also be made with foamedthermoplastic particles or beads, which may be made by such methods,molded in a thermoplastic matrix.

Customary additives can also be included in the thermoplastic materials,for example dispersants, antioxidants such as phenols, phosphites, andhydrazides, processing aids, surfactants, stabilizers, and so on. Thecover may also contain additives such as hindered amine lightstabilizers such as piperidines and oxanalides, ultraviolet lightabsorbers such as benzotriazoles, triazines, and hindered phenols,fluorescent materials and fluorescent brighteners, dyes such as bluedye, and antistatic agents.

The thermoplastic materials may be made by conventional methods, such asmelt mixing in a single- or twin-screw extruder, a Banbury mixer, aninternal mixer, a two-roll mill, or a ribbon mixer. The firstthermoplastic material is formed into a core center and the secondthermoplastic material is formed into a core layer around the corecenter by usual methods, for example by injection molding with a moldtemperature in the range of 150° C. to 230° C. If there is a second corelayer, the fourth thermoplastic material may be formed in a layer overthe core layer by the same methods. The molded core including corecenter, core layer, and optionally second core layer or further corelayers, may be ground to a desired diameter after cooling. Grinding canalso be used to remove flash, pin marks, and gate marks due to themolding process.

In some embodiments, particularly when the cover has a specific gravityof at least about 2 g/cm³, the core center has a diameter of from about28 mm to about 35 mm and preferably from about 30 mm to about 34 mm. Inother embodiments, particularly when the core layer and the cover eachhave a specific gravity of at least about 1.1 g/cm³, the core center hasa diameter of from about 21 mm to about 29 mm, and preferably from about23 mm to about 27 mm.

The core layer may have a thickness of at least about 4 mm. In certainpreferred embodiments, the core layer has a thickness of at least about5 mm. In various embodiments, the core layer may have a thickness offrom about 4 mm to about 8 mm.

A cover layer is molded over the core. In various embodiments, the thirdthermoplastic material used to make the cover may preferably include oneor more of thermoplastic polyurethane elastomers, thermoplastic polyureaelastomers, and the metal cation salts of copolymers of ethylene withethylenically unsaturated carboxylic acids.

The cover may be formed on the multi-layer core by injection molding,compression molding, casting, and so on. For example, when the cover isformed by injection molding, a core fabricated beforehand may be setinside a mold, and the cover material may be injected into the mold. Thecover is typically molded on the core by injection molding orcompression molding. Alternatively, another method that may be usedinvolves pre-molding a pair of half-covers from the cover material bydie casting or another molding method, enclosing the core in thehalf-covers, and compression molding at, for example, between 120° C.and 170° C. for a period of 1 to 5 minutes to attach the cover halvesaround the core. The core may be surface-treated before the cover isformed over it to increase the adhesion between the core and the cover.Nonlimiting examples of suitable surface preparations include mechanicalor chemical abrasion, corona discharge, plasma treatment, or applicationof an adhesion promoter such as a silane or of an adhesive. The covertypically has a dimple pattern and profile to provide desirableaerodynamic characteristics to the golf ball.

The cover has a thickness of at least about 1 mm in various embodiments,preferably at least about 2 mm in other embodiments. In general thecover may be from about 1 mm or from about 2 mm or from about 2.5 mmthick up to about 6 mm or up to about 5 mm or up to about 4 mm thick. Ifthere are two cover layers, typically, the cover layers may eachindependently have a thickness of from about 0.6 mm to about 2.0 mm,preferably from about 0.8 mm to about 1.6 mm.

In preferred embodiments, the golf ball is free from any thermosetrubber layer or other thermoset layer.

The golf balls can be of any size, although the USGA requires that golfballs used in competition have a diameter of at least 1.68 inches(42.672 mm) and a weight of no greater than 1.62 ounces (45.926 g). Forplay outside of USGA competition, the golf balls can have smallerdiameters and be heavier.

After a golf ball has been molded, it may undergo various furtherprocessing steps such as buffing, painting and marking. In aparticularly preferred embodiment of the invention, the golf ball has adimple pattern that coverage of 65% or more of the surface. The golfball typically is coated with a durable, abrasion-resistant andrelatively non-yellowing finish coat.

The description is merely exemplary in nature and, thus, variations thatdo not depart from the gist of the disclosure are a part of theinvention. Variations are not to be regarded as a departure from thespirit and scope of the disclosure

What is claimed is:
 1. A golf ball, comprising: a core center having adiameter of from about 28 mm to about 35 mm and a specific gravity of upto 0.95 comprising a first thermoplastic material having a firstflexural modulus of less than about 15,000 psi, wherein the core centeris foamed or comprises hollow glass particles; a core layer disposedradially outward from the core center comprising a second thermoplasticmaterial having a second flexural modulus of up to about 15,000 psi,wherein the second flexural modulus is greater than the first flexuralmodulus; and a cover disposed radially outward from the core layer,wherein the cover has a specific gravity of at least about 2, a thirdflexural modulus of at least about 15,000 psi, a thickness of at leastabout 2 mm, and comprises a third thermoplastic material, such that thespecific gravity of the cover is at least about 1.05 greater than thespecific gravity of the core center.
 2. A golf ball according to claim1, wherein the cover has a specific gravity of from about 2.0 to about3.0.
 3. A golf ball according to claim 1, wherein the specific gravityof the core center is from about 0.85 to about 0.95.
 4. A golf ballaccording to claim 1, wherein the specific gravity of the core layer isat least about 0.1 greater than the specific gravity of the core center.5. A golf ball according to claim 1, wherein the first flexural modulusis up to about 10,000 psi.
 6. A golf ball according to claim 1, whereinthe first flexural modulus is from about 3000 psi to about 6000 psi andthe second flexural modulus is from about 6000 psi to about 12,000 psi.7. A golf ball according to claim 1, wherein the third flexural modulusis at least about 35,000 psi.
 8. A golf ball according to claim 1,wherein the golf ball is free from a thermoset rubber layer.
 9. A golfball, comprising: a core center having a diameter of from about 21 mm toabout 29 mm comprising a first thermoplastic material having a firstflexural modulus of less than about 15,000 psi, a specific gravity of upto 0.95, and wherein the core center is foamed or comprises hollow glassparticles; a core layer disposed radially outward from the core center,wherein the core layer has a specific gravity of at least about 1.1 andcomprises a second thermoplastic material having a second flexuralmodulus of up to about 15,000 psi, wherein the second flexural modulusis greater than the first flexural modulus; and a cover disposedradially outward from the core layer, wherein the cover has a thicknessof at least about 1 mm, has a specific gravity of from about 2.0 toabout 3.0, and comprises a third thermoplastic material having a thirdflexural modulus of at least about 15,000 psi, such that the specificgravity of the cover is at least about 1.05 greater than the specificgravity of the core center.
 10. A golf ball according to claim 9,wherein the specific gravity of the core center is from about 0.85 to0.95.
 11. A golf ball according to claim 9, wherein the first flexuralmodulus is up to about 10,000 psi.
 12. A golf ball according to claim 9,wherein the first flexural modulus is from about 3000 psi to about 6000psi and the second flexural modulus is from about 6000 psi to about12,000 psi.
 13. A golf ball according to claim 9, wherein the thirdflexural modulus is at least about 35,000 psi.
 14. A golf ball accordingto claim 9, wherein the golf ball is free from a thermoset rubber layer.15. A golf ball according to claim 9, wherein the cover comprises afiller selected from the group consisting of metals and metal oxides.